The present invention relates to writing instruments and more particularly to a writing instrument having a mechanism for advancing the writing tip of the instrument from the instrument barrel for employment of the writing instrument and retracting the writing tip to a point within the barrel when the instrument is not in use.
Various writing instruments, such as pencils or ball point pens, are known in which the writing tip is advanced or retracted relative to the barrel by means of rotating or pushing the external elements on the barrel of the instrument. Typical of these advance-retract devices are U.S. Pat. No. 3,679,318, issued Jul. 25, 1972, to Thomas A. Liguori; U.S. Pat. No. 4,290,707, issued Sept. 22, 1981, to Tatsuo Ariga; U.S. Pat. No. 4,786,197, issued Nov. 22, 1988, to Harold E. Koeln et al.; French patent 1004813, published Apr. 3, 1952, in the name of Poursier; and British patent specification 934160, published Aug. 14, 1963, in the name of Ronald Hare. These and other such devices have been disclosed, and a wide variety of devices of this type have been produced and met with commercial success.
It has been found that many of these devices require in their assembly a variety of fastening elements such as threaded screws, rivets or the like to complete the assembly. The employment of threaded elements, rivets, etc. effectively increases the cost of the writing instrument both from a standpoint of materials as well as labor, during assembly.
In view of the foregoing therefore it is an object of the invention to provide a writing instrument having an advance-retract mechanism containing a minimal number of parts which may be inexpensively produced.
A further object of the invention is to provide a writing instrument having an advance-retract mechanism which is simple in construction and more easily and economically assembled than those of the prior art.
Yet another object of the invention is to provide a writing instrument which is economical to produce, efficient in operation and easily adaptable to mass production techniques.